SQL Server offers a very simple but effective solution for scaling read-only databases upto a maximum of 8 instances. Oracle RAC achieves the same at a higher cost point and also provides for read/write capabilities that may not be needed for most customers interested in read-only scaling. For a data mart where database is extracted periodically from the contents of a data warehouse and is used for reporting there is no need for read-write scaling, read-only scaling is good enough.
For Analysis Services needing to spread the query load across multiple servers to accomodate the increasing number of concurrent users one should consider NetScaler DataStreamTM for the SQL server scaling/load balancing needs. With Microsoft SQL Server Enterprise and NetScaler DataStreamTM one can achieve even load distribution, single SQL connection string to the clients, superior health monitoring and most of all a cost-effective solution vs Oracle RAC for read-only data mart or data warehouses.
With NetScaler DataStreamTM acting as a full SQL Proxy, customers can advertise a single IP for all of their SQL infrastructure. Advanced content switching capabilities of NetScaler DataStreamTM can parse and interpret SQL queries distinguishing between reads( SELECT) and writes (insert, update, etc), empowering the DBA to decide where to run reporting/OLTP work loads without exposing the infrastructure to the SQL clients.
For more details on NetScaler DataStreamTM please visit http://www.citrix.com/English/ps2/products/subfeature.asp?contentID=2309522.
For more details on Scalable shared databases please look into http://support.microsoft.com/kb/910378